It sounds gimmicky, or like a nice hobby at best: building a sperm bank to someday restore coral reefs worldwide.

But a collection of one trillion (and counting) frozen coral sperm being collected by Dr. Mary Hagedorn of the Hawaii Institute of Marine Biology, is anything but a hobby: It could someday have a huge impact on economies and human health.

After all, coral reefs provide millions of people with food as well as jobs in tourism, recreation and fishing. They also protect shorelines against waves, storms and floods -- and they do so much more cheaply (and more beautifully) than any man-made buffer. Finally, coral reefs, also known as the "medicine cabinets" of the 21st century, are the source of medicines being developed to treat diseases ranging from cancer to viruses.

Why build a sperm bank for corals, which have been around as long as man, and how would it work?

Why a coral sperm bank now?

Coral bleaching events -- in which stressed corals expel the algae that make them so colorful and then turn completely white -- are becoming much more frequent throughout the world and even lasting so long that whole reefs cannot recover.

The buildup of carbon dioxide in the ocean is acidifying them, weakening the "bones" of reefs, which are composed of calcium-carbonate. Acidification of ocean water is also inhibiting the growth of coral skeletons.

Overfishing, high water temperatures and disease outbreaks have already killed 80% of the Caribbean's corals, and are also destroying corals in the Pacific.

The extent of living coral in the central and western areas of the Pacific shrank by half between the early 1980s and 2003. If the problems afflicting coral continue, about half the world's corals will be destroyed by 2050.

Details on the coral sperm bank

The trillion coral sperm in Dr. Hagedorn's sperm bank, collected from corals in Hawaii, the Caribbean and Australia, could fertilize anywhere from 500 million to one billion coral eggs.

Dr. Hagedorn, who is a reproductive physiologist with the Smithsonian Institution, has also collected three billion frozen embyronic cells, some of which could act as stem cells and grow into adult corals.

In case you're reading this thinking, but hey, coral can reproduce asexually! Yes, you are correct -- with a fragment of coral, you can create a clone of the parent.

However, sexual reproduction is necessary to keep the coral population genetically diverse -- and to make it strong enough to withstand the challenge of climate change.

Other methods of preserving corals

A coral sperm bank isn't the only solution against the ills suffered by corals. Conservationists are also working to establish fishing regulations and create marine reserves that protect reefs.

But just a smidgen over a quarter of the world's reefs are in reserves, and enforcement within reserves is spotty. Some marine biologists are also working to raise coral in captivity and the introduce them to natural habitats.

But these measures can only go so far against climate change. Nancy Knowlton, a well-known coral-reef biologist at the Smithsonian, told The Times:

“Protecting fish communities, making sure water quality is good, all of those efforts can buy decades of time. But if we continue on this greenhouse-gas emissions trajectory, the only place we’re going to be able to find many corals will be in Mary’s freezers.”

The importance of the coral sperm bank

Dr. Hagedorn sometimes has to wait and wait to capture the sperm, in case the spawning schedule veers from its expected timeline. But when that happens, she reminds herself that her patience will have been rewarded if she is able to do for corals what JoGayle Howard, a National Zoo researcher, did for ferrets: inseminate a female ferret with sperm collected and frozen more than 20 years earlier, adding more genetic diversity to an endangered species.

As she told The Times about the importance of each vial: “Think about the black-footed ferret. Just a few individuals can get a population started again.”